The Field of the Invention relates to the drilling, completion and production of wells drilled into formations containing heavy, viscous hydrocarbons. These hydrocarbons may be referred to as bitumen or tar. The invention relates to the drilling of a well bore substantially vertically downwardly, then curving the well bore out into a substantially horizontal portion, then thermal treatment and production of the viscous hydrocarbons from the producing formation.
The heavy, viscous hydrocarbons are valuable for refining. The refined products can be used as the basis for road paving and plastics. Such formations as may be near the earth surface can be strip mined to recover the hydrocarbons. Many producing zones, however, are deeper, and may be a few hundred feet or several thousand feet below the earth surface. For purposes of this specification, producing zone and producing formation have the same meaning. For purposes of this specification, tubing placed in a well casing may also be referred to as a tubing string, and surface means at or near the earth surface unless otherwise referenced.
Heavy hydrocarbon, also known as heavy crude oil, can have American Petroleum Institute (API) density from about 8 up to 20 or more. Lower API density numbers indicate greater specific gravity. API 10 has a specific gravity of 1. Such heavy crude oils are very viscous, and are essentially solid at in situ (in place) temperatures.
Recovery of such heavy crude oil has been accomplished in the past by heating. Steam is been injected through a well into a producing formation for a time, then the well is produced.
This process is referred to as the "huff and puff" method. With several vertical wells drilled into a zone, several wells may be produced with the "huff and puff" process. After sufficient oil has been removed from the formation, communication may be established from one well to another. Then a continuous flood of steam may be injected into one well. A mixture of heated oil, condensate and steam may then be produced from an adjacent well. This process is known a continuous steam flood.
The Related Prior Art includes U.S. Pat. No. 4,565,245, in which Mims et al. teach the method and apparatus of a system of single well completion for carrying a hot stimulating agent into a tar sand from the remote end of the well. A progressively movable barrier is used to extend the flow path pattern in the producing formation. No provision is made to lift fluids from the remote end of the casing. The use of a barrier in the casing indicates the use of a heated flooding process rather than the use of heat conduction in combination with gravity in this invention to cause hydrocarbons to flow to the well bore. Mims also teaches that movement of the barrier is needed during the producing life of the formation.
In U.S. Pat. No. 4,640,359, Livesay teaches the method and apparatus for use in a single well for conducting a hot thermal stimulating medium to the remote end of the well. An expandable diverter forms a barrier which is progressively lengthened to cause the stimulating medium to sweep progressively increasing lengths of the producing formation.